LT3519EMS-1 查看數據表（PDF） - Linear Technology

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LT3519EMS-1

LED Driver with Integrated Schottky Diode

Linear Technology 

LT3519/LT3519-1/LT3519-2

APPLICATIONS INFORMATION

Inductor Selection

The inductor used with the LT3519/LT3519-1/LT3519-2

should have a saturation current rating of 1A or greater.

For buck mode LED drivers, the inductor value should be

chosen to give a ripple current 150mA or more. In the

buck mode, the inductor value can be estimated using

the formula:

L

(µH)

=

( ) DBUCK • VIN – VLED

fOSC (MHz) • 0.15A

⎛

⎝⎜

µH

•

A•

V

MHz

⎞

⎠⎟

DBUCK

=

VLED

VIN

VLED is the voltage across the LED string, VIN is the input

voltage to the converter, and fOSC is the switching frequency.

In the boost configuration, the inductor can be estimated

using the formula:

L

(µH)

=

DBOOST • VIN

fOSC (MHz) • 0.15A

⎛

⎝⎜

µH

•

A•

V

MHz

⎞

⎠⎟

( ) DBOOST =

VLED – VIN

VLED

Table 1. Recommended Inductor Vendors

VENDOR

PHONE

Sumida

(408)321-9660

Toko

(408)432-8281

Cooper

(561)998-4100

Vishay

(402)563-6866

WEB

www.sumida.com

www.toko.com

www.cooperet.com

www.vishay.com

Input Capacitor Selection

For proper operation, it is necessary to place a bypass

capacitor to GND close to the VIN pin of the LT3519/

LT3519-1/LT3519-2. A 1μF or greater capacitor with low

ESR should be used. A ceramic capacitor is usually the

best choice.

In the buck mode configuration, the capacitor at the input

to the power converter has large pulsed currents. For

best reliability, this capacitor should have low ESR and

ESL and have an adequate ripple current rating. A 2.2μF

ceramic type capacitor is usually sufficient for LT3519

(400kHz version). A capacitor of proportionately less

value for LT3519-1/LT3519-2 (higher frequency version)

can be used.

Output Capacitor Selection

The selection of output capacitor depends on the load

and converter configuration, i.e., step-up or step-down

and the operating frequency. For LED applications, the

equivalent resistance of the LED is typically low, and the

output filter capacitor should be sized to attenuate the

current ripple.

To achieve the same LED ripple current, the required filter

capacitor value is larger in the boost and buck-boost mode

applications than that in the buck mode applications. Lower

operating frequencies will require proportionately higher

capacitor values. For LED buck mode applications, a 1μF

ceramic capacitor is usually sufficient. For the LED boost

and buck-boost mode applications, a 2.2μF ceramic ca-

pacitor is usually sufficient. Very high performance PWM

dimming applications may require a larger capacitor value

to support the LED voltage during PWM transitions.

Use only ceramic capacitors with X7R, X5R or better dielec-

tric as they are best for temperature and DC bias stability

of the capacitor value. All ceramic capacitors exhibit loss

of capacitance value with increasing DC voltage bias, so

it may be necessary to choose a higher value capacitor

to get the required capacitance at the operation voltage.

Always check that the voltage rating of the capacitor is

sufficient.

Table 2. Recommended Ceramic Capacitor Vendors

VENDOR

PHONE

WEB

TDK

(516)535-2600

www.tdk.com

Kemet

(408)986-0424

www.kemet.com

Murata

(814)237-1431

www.murata.com

Taiyo Yuden

(408)573-4150

www.t-yuden.com

3519fa

11

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